A large amount of information is routinely processed in the field of computers and hard disk drives (HDDs) are used as one type of information storage apparatus for recording and playing back such a large amount of information. A typical HDD includes a magnetic disk, which is a disc-shaped storage medium on which information is recorded in a state where the magnetic material is magnetized, and a magnetic head for recording information on the magnetic disk and playing back information.
The magnetic head applies the magnetic field corresponding to information to be recorded to the magnetic disk to record the information and detects a weak magnetic field emitted from the magnetized magnetic material in the magnetic disk to play back the information. The magnetic head is mounted on a head slider, which is a metal block, and the above processing is performed in a state where the head slider is floated over the magnetic disk, that is, the magnetic head is floated over the magnetic disk. The flying height of the portion where the magnetic head is mounted on the head slider from the magnetic disk in the recording or playback of information may vary due to, for example, the air flow between the surface of the magnetic disk rotating at high speed and the head slider. Excessive variation in the flying height of the portion where the magnetic head is mounted on the head slider undesirably causes degradation in the quality of the information that is recorded or played back.
The head slider is generally shaped such that the flying height of the entire head slider from the magnetic disk is stabilized. However, head sliders have been reduced in size in recent years and, therefore, it is difficult to stabilize the flying heights only by modifying the shapes of the head sliders.
The magnetic head is provided with a coil to generate the magnetic field for the recording of information. It is known that a phenomenon called Thermal Pole Tip Protrusion (TPTP) is caused in the recording of information, in which the portion where the magnetic head is mounted on the head slider is thermally expanded due to Joule heat caused by a current flowing through the coil. The expansion decreases the flying height of the portion where the magnetic head is mounted on the head slider from the magnetic disk (for example, refer to Japanese Patent No. 3927538).
In order to precisely control the flying height so as to be stabilized by positively utilizing the TPTP, for example, a flying-height control mechanism is proposed, in which a heater is embedded in the head slider, the TPTP is caused by heat generated by the heater, and the portion where the magnetic head is mounted on the head slider is precisely protruded toward and away from the surface of the magnetic disk to adjust the flying height of the portion where the magnetic head is mounted on the head slider.
Computers are used in various environments in recent years owing to the prevalence of the computers. The flying height of the head slider, described above, is strongly affected by the air pressure in the corresponding computer. When the air pressure in the computer is low because, for example, the computer is used at a higher altitude, the flying height of the head slider is generally lower than the flying height at normal air pressure. Accordingly, the adjustment of the flying height of the portion where the magnetic head is mounted on the head slider in the same manner as at the normal air pressure by such a flying-height control mechanism when the air pressure in the computer is very low can cause the portion where the magnetic head is mounted on the head slider to be too close to the magnetic disk. In an extreme case, a problem can be caused in which the portion where the magnetic head is mounted on the head slider contacts the magnetic disk.
It is desirable to keep track of the air pressure in the computer in order to adjust the flying height of the portion where the magnetic head is mounted on the head slider in accordance with such variation in the air pressure. Technologies for keeping track of the air pressure in the computer in related art include a technology in which the air pressure in the computer is calculated from the value of an operating current to a spindle motor rotating the magnetic disk based on the fact that the operating current to the spindle motor is affected by the viscosity of the air depending on the air pressure (for example, Japanese Unexamined Patent Application Publication No. 2002-150744), and a technology in which the air pressure in the computer is calculated from the value of an operating current to a mechanism for fixing the head slider at a certain position on the magnetic disk against the rotation of the magnetic disk based on the fact that the operating current to the mechanism is affected by the viscosity of the air depending on the air pressure (for example, refer to Japanese Patent No. 2983009).
However, it is not possible to precisely control the flying height of the portion where the magnetic head is mounted on the head slider by using the slight thermal expansion of the head slider with the methods disclosed in the above patent documents.